<!DOCTYPE html>
<html>
<head>
  <style>
    H1 {
      text-decoration: underline;
    }
    h1 {
      border: 1px solid blue;
    }
    H1 {
      color: red;
    }
    h1[ID='hamburg'] { background-color:purple;}
    h1[id='HAMBURG'] { background-color:green;}
    h1[hamburg='tokyo'] { opacity:0.4; }
  </style>
</head>
<body>
  <h1 id='hamburg' hamburg="TOKYO">This sentence should be written in red, underlined, have a purple background, 100% opacity and a 1px solid blue border.</h1>
</body>
</html>
